8. Tonography Tonographic outflow facility (C) will be performed using an electronic Schiøtz tonographer (Model 720, Berkeley Bioengineering Inc, USA) at 10AM. The facility of outflow will be calculated from the rate of decay of intraocular pressure in the supine position during application of a recording Schiøtz tonometer over a period of 4 minutes with a standard 5.5 gram weight. The "R" values of the curve at every 30-second time point will be manually entered into the McLaren tonography computer program. The program fits a second-degree polynomial by least squares to the nine data points and determines the best-fit values for time 0 and time 4 minutes by extrapolation.